Add centralized path to mypy.ini in crc32c

Add the centralized path to the root `mypy.ini` file for these packages:

- [x] ~bigframes~ obsolete, code moved to github.com/google/bigframes
- [ ] google-cloud-crc32c

Use the following path search:

```
# Path to the centralized mypy configuration file at the repository root.
# Search upwards to support running nox from both monorepo packages and integration test goldens.
MYPY_CONFIG_FILE = next(
(
str(p / "mypy.ini")
for p in CURRENT_DIRECTORY.parents
if (p / "mypy.ini").exists()
),
str(CURRENT_DIRECTORY.parent.parent / "mypy.ini"),
)
```

[See this PR for exemplars](https://github.com/googleapis/google-cloud-python/pull/17409)